1. Field of the Invention
This invention relates to an arrangement for improving the transfer of heat between a heat source and a heat sink, and, more particularly, between a power transistor and its adjacent heat sink.
2. Description of the Prior Art
In order to improve the performance characteristics of temperature sensitive devices, such as semi-conductors and power transistors in particular, the power transistors are generally mounted to a heat dissipation device such as a heat sink. However, it has been found that when mounting a power transistor in what is commonly known as a TO.sub.3 type package to a standard heat sink, inasmuch as adjacent surfaces of the transistor and heat sink have high and low spots, no more than 5 to 10 percent of the overlapping area therebetween is actually ever in contact. This minimal direct surface contact results in a limitation on the amount of heat that can be transferred from the power transistor to the heat sink, and severely restricts the thermal efficiency of the overall arrangement. The maximum power level at which the power transistor can be operated when using power transistors in, for example, pulse-width modulated servo drive systems, is thereby limited, and the amount of drive which can be delivered to a servo motor is also limited. Thus the overall system becomes limited simply because the power generated by the transistor cannot be efficiently dissipated. One method of improving the efficiency of the transfer of heat from the power transistor to the heat sink has been to apply liquid silicone grease to the surface area between the transistor and heat sink. While it has been observed that this may result in an improvement in heat transfer between the power transistor and the heat sink, in view of the liquid nature of the material, the silicone grease has been noted to drip onto electrical contact areas to which the power transistor is to be connected, thereby resulting in a degradation of the electrical performance of the circuit using the power transistors.